Azeotropic distillation of ketone-containing alcohols



AZEOTROPIC DISTILLATION OF KETONE-CQNTAINING ALCOHOLS v. F. MICHAEL Nov. 11, 1952 Filed Aug. 2. 1947 Lm qg LQ QFxCM M 0 W mtoxmvx M a MM 4. m r M Aw m QM W m Q4 m Q L LQ E mt B 5 3: 3

Q8 33% km Patented Nov. 11, 1952 AZEOTROPIC DISTILLATION OF KETONE- CONTAINING ALCQHOLS Vesta F. Michael, Tulsa, kla., assignor to Stanolmd Oil and Gas Company, Tulsa, Okla., a corporation of Delaware Application August 2,1947, Serial No. 765,741

9 Claims. (Cl. 202-42) Thisinvention relates to the purification of alcohols, and more particularly to a method for the preparation of substantially pure alcohols 50m mixtures thereof with methyl propyl kene. My invention broadly comprises a process for separating ethanol or n-propyl alcohol from mixtures thereof with methyl propyl ketone by fractional distillation with a hydrocarbon liquid havinglsuitable characteristics as hereinafter defined. By .this means, I am able to withdraw an overhead fraction containing substantially none of the methyl propyl ketone, and I may thereafter separate a substantially pure alcohol product from said overhead fraction by suitable means.

Numerous methods have been devised in the prior art for producing alcohols from various raw I materials. For example, in the so-called Fischer- Tropsch process, wherein carbon monoxide is hydrogenated over a suitable catalyst, the principal product is a mixture of hydrocarbons; but a substantial quantity of oxygenated compounds, including alcohols, ketones, aldehydes, carboxylic acids, and phenolic compounds, are also produced,

particularly when the reaction is carried out in the presence of an iron catalyst containing an alkaline promoter. Higher proportions of alcohols are produced by the so-called Synol process, which is a modified IFlscher-I'ropsch process, operated at higher pressure and lower temperature, for example, around 18-25 atmospheres and: 375-400 F. Mixed oxygenated compounds have also been produced by numerous processes in which hydrocarbons are subjected to an oxidation treatment.

'Inall of the various processes for producing 2 oxygenated substances, the isolation of individual compounds is a difficult problem, -owing to the large number of components in the product mixn-propyl alcohol from mixtures containing methyl proyl ketone by fractional distillation, for

example, of the crude products produced in one, 'of the processes noted above, the resulting alcohol fractions ordinarily contain up to around 5% or more by volume of the ketone, depending on the concentration of ketone in the starting material and on the efficiency of the fractionating means. The concentration of contaminating ke- 2 tone can be reduced to as low as around 1% by volume by employing fractionating equipment of high efliciency and by operation at high reflux ratios, but cannot be reduced substantially below this figure by ordinary methods, owing to the existence of azeotropic mixtures. In this situation, I have discovered that ethanol and n-propyl'alcohol can be separated substantially completely from the undesired ketone by fractional distillation in the presence of a suitable entrainer liquid, the alcohol or alcohols being taken off overhead as azeotropic mixtures with the entrainer liquid, substantially free from the ketone. The alcohol or alcohols may subsequently be recovered from the distillate in any desired degree of purity, by well-known means, such as by extractive distillation, by azeotropic distillation with water; or by extraction with a suitable solvent, followed by fractional distillation.

In a preferred form of my invention, I sub J'ect a mixture of ethanol and/or n-propyl alcohol containing methyl propyl ketone to fractional distillation in the presence of water and a suit able entrainer liquid. A heterogeneous stream, containing the alcohol, water, and entrainer liquid, with substantially none of the undesired ketone, is taken off overhead and separated into phases. The aqueous phase, containing most of the alcohol and a minor proportion of entrainer liquid, is withdrawn for further processing to isolate the alcohol; and the entrainer-liquid phase is recycled to the fractionating column. A mixture of entrainer liquid, ketone, and any residual water is ultimately withdrawn from the bottom of the fractionating column.

Entrainer liquids for use in my process should form a binary constant-boiling mixture with the alcohol that is to be purified, and a ternary constant-boiling mixture, preferably heter ogeneous. with water and alcohol. Moreover, the aqueous phase of the heterogeneous ternary constant-boiling mixture should preferably contain a substan-v tial proportion of the alcohol distilled overhead. in order to minimize the heat utilization per unit of product. The entrainer liquid preferably should not form a constant-boiling mixture with the ketone impurity; but if it does form such a constant-boiling mixture, the boiling point thereof should be sufficiently far above the boiling points of the binary entrainer-alcohol constantboiling mixture and of the ternary entrainer-alcohol-water constant-boiling mixture to permit their separation by fractional distillation. In general, hydrocarbon liquids which are stable and unreactive under the conditions employed in the fractionation, and which boil within the range of about 50 to 150 C. are suitable as entrainer liquids for use in my process. Among such liquids are aliphatic hydrocarbons, such as hexanes, hexenes, heptanes, heptenes, octanes, octenes, nonanes, nonenes, and mixtures thereof, such as petroleum naphthas; cycloaliphatic hydrocarbons, such as cyclopentane, methylcyclopentane, cyclohexane, methylcyclohexane and the like; and aromatic hydrocarbons, such as benzene, toluene, and xylene.

In carrying out my process, I prefer first to separate a comparatively narrow-boiling fraction of ketone-contaminated ethanol and/or n-propyl alcohol. I then introduce this fraction, .together with entrainer liquid and optionally with water, into a suitable fractionating still, and subsequently carry out the distillation as described above. I prefer to operate at ordinary pressures, but somewhat elevated and reduced pressures are also operative. .Imay introduce .additional entrainer liquid .from time to time to make up for losses fromlthestill, and .I may add water or steam, eithe -continuously or intermittently, in order to maintainadesired proportion of water in .the still system during .the distillation. .My process .may he carried out satisfactorily in either batch-type or continuous .equipment. The aqueous ketone-free alcohol solution that is withdrawn overhead from the heterogeneous constant-boiling mixture obtained in the preferred form of my invention may subsequently be subjected to a second distillation to separate a ternary heterogeneous azeotrope containing entrainer, water, and alcohol, .05? which the aqueous phase may be refluxed, and the entrainer phase may be returned to the first distillation step. The bottoms from the second distillation step, now free of both entrainer and ketone, may be subjected .to further processing steps, well known in the art, 'to .recover alcohol of any .desired purity.

My invention may be more fully understood from the following examples:

Example I The aqueous phase from aFischer-Tropsch process, employing an .alkali-promotedironcatalystywas carefully fractionated, and a fraction was isolated boiling between 77 and 78 C. and having the :following properties:

'Per cent by I weight Ethanol 93.4% Methyl propyl ketone i- 1.50 Water 4.75 Ester, :as ethyl propionate 0.31 Acidity, as acetic acid 0.003

Specific gravity, D4 -C 0.7996 Refractiveindex, 11 1.36308 'A mixture containing 200 parts by volume of the I I-78 C. fraction, 150 parts by volume of heptane, and additional water was fractionated in a batch still, and a heterogeneous ternary constant-boiling mixture boiling at 68.2" C. and having the following composition was taken off overhead:

Per cent by volume .Heptane 63.50 Ethanol 30.35 Water 6.15

Ratio :(in distillate) of organic to aque ous phase:

The ethanol recovered from the aqueous phase of the constant-boiling mixture gave no precipitate with 2,4-dinitrophenylhydrazine, and was therefore substantially free from methyl propyl ketone.

Example II V A Fischer-Tropsch ethanol fraction boiling between 77 and 79 C. was found to contain the following impurities:

Per cent by volume Methyl propyl ketone 1.09 Water 4.48

A mixture of 767 parts by volume of the 77-79" C. fraction and 460 parts by volume of benzene was distilled through a fractionating column. A heterogeneous fraction, containing benzene, ethanol, and water, was distilled overhead in the range of to C., andon being tested with 2,4-dinitrophenylhydrazine was found to be substantially free from carbonyl compounds.

Example III Heptane 68.6% byweight n-Propyl alcohol 19.8% by weight Water 11.6% by weight Ketones none Ratio (in distillate.) of organic to aqueous phase: 5.31% by volume The overhead stream is condensed in condenser I2, from'which it flows to separator l3 and forms two layers. The upper layer, comprising principally heptane and n-propyl alcohol with a trace of water, is refluxed byway of line M to the top of fractionator II. The bottom layer in separator l3 consists of n-propyl alcohol, water, and a trace of.-heptane, and is substantially :free from ketones. This layer is introduced through heater l5 intofractionating column It at an intermediate point, and the traces of heptane distillcverhead as .a ternary azeotrope with water and .n-propyl alcohol. This azeotrope is condensed in cooler 17 and led .into separator l8. From separator [8, the heptane (upper) layer is :refluxed to the top of fractionator II by way of line 14,, and the aqueous (lower) layer is refluxed to the top of fractionator it. A heptanefree solution of n-propyl alcohol and water is withdrawn from the bottom of fractionator l6 and is fed by. pump [.9 through heater '20 into fractionator 2| at an intermediate point. A wet n-propylalcohol fraction, substantially free from ketones .and heptane, is distilled overhead from fractionator 2! through cooler 22 into reflux bottle 23,, .from which a portion is refluxed to the .fract'ionator through valve 24, and the remainder is taken oif through valve 25. The stripped water stream from the bottom of fractionator 2| is removed through line 26 and discarded or returned to process.

Thebottoms from fractionator ll, comprising ketones, heptane, and water, may be subjected to .further processing to recover the various components.

While the above examples illustrate the preferred forms of my invention, it will be understood that departures may be made therefrom within the scope of the specification and claims. In particular, it is to be understood that my process is applicable to the purification of ethanol and n-propyl alcohol solutions contaminated with methyl propyl ketone, from whatever source derived. In general, it may be said that any modifications or equivalents that would ordinarily occur to those skilled in the art are to be considered as lying within the scope of my invention.

In accordance with the foregoing specification, I claim as my invention:

1. A process for separating ethanol from a mixture consisting essentially of ethanol and methyl propyl ketone which comprises fractionally distilling said mixture in the presence of water and a hydrocarbon selected from the group consisting of Cs and C7 hydrocarbons and Cs aliphatic hydrocarbons, and withdrawing overhead a ternary azeotrope of ethanol, water and hydrocarbon.

2. The process of claim 1 wherein said hydrocarbon liquid comprises primarily benzene.

3. The process of claim 1 wherein said hydrocarbon liquid comprises primarily Cq hydrocarbons.

4. A process for separating n-propyl alcohol from a mixture consisting essentially of n-propyl alcohol and methyl propyl ketone which comprises fractionally distilling said mixture in the presence of Water and a hydrocarbon selected from the group consisting of C6 and C1 hydrocarbons and Ca aliphatic hydrocarbons, and withdrawing overhead a ternary azeotrope of said hydrocarbon, water and n-propyl alcohol.

5. The process of claim 4 wherein said hydrocarbon liquid comprises primarily benzene.

6. The process of claim 4 wherein said hydrocarbon liquid comprises primarily C7 hydrocarbons.

7. The process of claim 4 wherein said hydrocarbon comprises primarily heptane.

8. In a process for separating a purified alcohol from a mixture consisting essentially of methyl propyl ketone and an alcohol selected from the group consisting of ethanol and n-propyl alcohol, the steps which comprise fractionally distilling said mixture in the presence of water and a hydrocarbon selected from the group consisting of Ca and C1 hydrocarbons and Ca aliphatic hydrocarbons, and separating overhead a ternary azeotrope of said alcohol, water and hydrocarbon.

9. In a process for the separation of a lower aliphatic alcohol from an aqueous mixture, the organic components of which consist essentially of methyl propyl ketone and a lower aliphatic alcohol selected from the group consisting of ethanol and l-propanol, the steps which comprise adding a hydrocarbon selected from the group consisting of Cs and C7 hydrocarbons and Ca aliphatic hydrocarbons to said mixture and thereafter subjecting the latter to distillation whereby said alcohol is removed from said mixture in the form of a ternary azeotrope with said hydrocarbon and water and continuing said distillation until the residue in the still which consists essentially of anhydrous methyl propyl ketone is substantially free from said alcohol.

VESTA F. MICHAEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Germany Aug. 10, 1915 

8. IN A PROCESS FOR SEPARATING A PURIFIED ALCOHOL FROM A MIXTURE CONSISTING ESSENTIALLY OF METHYL PROPYL KETONE AND AN ALCOHOL SELECTED FROM THE GROUP CONSISTING OF ETHANOL AND N-PROPYL ALCOHOL, THE STEPS WHICH COMPRISE FRACTIONALLY DISTILLING SAID MIXTURE IN THE PRESENCE OF WATER AND A HYDRO- 